Many diet experts recommend that people looking to lose weight should replace their dinner plates with appetizer-sized plates, which will help them decrease their portion size. But results from five different studies conducted by researchers suggest that both size and the contrast in the color of foods to the plate influence how much a person eats.

The researchers based their studies on an optical illusion theory described by the 19th century philosopher Franz Delboeuf. Delboeuf observed that if two circles the same size were placed inside two other circles that were different sizes, the same-sized inner circles would also seem to be different sizes.

The studies involved nearly 200 participants, ages 18 to 39, who were served different-sized plates filled with food. Those who were given larger plates filled their plates with more food than those with smaller plates. Those who were served food on tables with a higher color contrast between the plates and the tablecloth also ate more than those who were served the same amount of food without a noticeable contrast.

“Someone who owns a larger dinnerware in different colors may want to choose the color that highly contrasts with the food he is serving to minimize overserving biases,” the researchers wrote in their paper.

Removing the contrast eliminated the illusion of an outside circle that, based on Delbeouf’s theory, would make the plate seem fuller. Just because those with smaller plates and less color contrast ate less, they still seemed to feel satisfied, the researchers said.

“It could simply lead consumers to satisfy their hunger while unknowingly eating less,” the researchers wrote. “It may be easier to change our personal environments than to change our minds.”